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Chemistry > Energy changes > Flashcards

Energy changes Flashcards

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1
Q

What is an exothermic reaction

A

When energy is given out to the surroundings

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2
Q

What is an endothermic reaction

A

When energy is taken in from the surroundings

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3
Q

If rectants have more energy than products, what type of reaction is it

A

Endothermic

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4
Q

What is breaking bonds
Exo or endo

A

Endothermic

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5
Q

What are two examples of an exothermic reaction

A

Burning fuels- Combustion
Neutralisation (Acid + Alkali–> Salt + Water)

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6
Q

What is an example of an endothermic reaction

A

Thermal decomposition

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7
Q

What is a real life use of exothermic reactions

A

Instant hand warmers

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8
Q

What is a real life use of endothermic reactions

A

Instant sports ice packs

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9
Q

If there is an exothermic reaction on a graph, will the line be above or below the initial point

A

Below

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10
Q

What is the peak amount of energy reached during a reaction called

A

Activation energy

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11
Q

What do you need to break bonds

A

Energy/ heat

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12
Q

What is released when new bonds form

A

Energy

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13
Q

What is an electrochemical cell

A

A system where there are two different electrodes in contact with an electrolyte.

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14
Q

What are the electrodes typically made out of

A

Metals

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15
Q

What is an electrolyte

A

A liquid that is able to carry charge. It contains ions that react with the electrodes

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16
Q

How does a simple battery work

A

The chemical reactions between the electrodes (which are connected at the top) and the electrolyte set up a charge difference between the electrodes.

This means electricity will flow from the more reactive metal to the less reactive metal.

17
Q

What does the voltage of a cell depend on

A
  • The metals used
  • The type of electrolyte
18
Q

What is a battery and how do you make one

A

A battery is two or more cells connected in series
You can make a battery by connecting different cells

19
Q

Why do sime batteries run out of charge

A

Because all of the reactants are used up and the reaction is irreversible

20
Q

What type of batteries are non rechargeable and why

A

Alkene batteries are non renewable
This is because te reaction is irreversible

21
Q

How are rechargeable batteries recharged

A

The reaction is reversed by connecting an external electric current

22
Q

What is a fuel cell

A

An electrical cell that is supplied with fuel and oxygen
Uses energy from the reaction to produce electrical energy

23
Q

What happens to fuel when it enters the fuel cell

A

The fuel is oxidised. This sets up a potential difference within the cell

24
Q

What are the reactants and products in a hydrogen fuel cell

A

Reactants:
Hydrogen and oxygen
Products:
Water and energy

25
Q

How is a hydrogen fuel cell set up

A

Electrolyte (potassium hyroxide) in the middle
Carbon Anode (negative) on the left
Carbon Cathode (positive) on the right
REVERSE OF ELECTROLYSIS
Both electrodes have inlets on the sides
Hydrogen goes into anode
Oxygen goes into cathode
All water and heat leaves through outlet of cathode

26
Q

How does a hydrogen fuel cell work

A

Hydrogen comes in and is oxidised by anode
Hydrogen becomes an ion
Electrons pass around the wire to the cathode, while the hydrogen moves through the electrolyte to the cathode
Electrons and hydrogen ions react with oxygen to produce water
Water leaves by outlet

27
Q

What is the half equation of oxidation of hydrogen in fuel cells

A

H₂ —> 2H(+) + 2e(-)

28
Q

What is the half equation of the reaction of hydrogen ions and water at the positive electrode

A

O₂ + 4H(+) + 4e(-) –> 2 H₂O

29
Q

What is the overall equation in a fuel cell

A

2H₂ + O₂ —> 2H₂O

30
Q

What are some advantages of hydrogen fuel cells

A
  • Less polutants/ emissions
  • More reusable than electric batteries
  • Cheaper than electricc batteries
  • Can store more energy than typical batteries
31
Q

What are some disadvantages of hydrogen fuel cells

A
  • Hydrogen is a gas so it takes up more space
  • Hydrogen is explosive so must be handled with care
  • Hydrogen is made from electrolysis which uses energy that could be releasing emissions

Chemistry (10 decks)

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